Optical filters have been used in glazings in window technology to control the flow of light and heat through the glazing. Such filters may be used on any sort of window, including those in buildings, vehicles, aircraft, spacecraft, ships or the like. Optical filters have also been used to regulate lighting and heating levels, for glare reduction, and energy load management. As an example, buildings consume over one third of all energy and over two-thirds of the electricity used in the United States, and are responsible for about one third of all greenhouse gas (GHG) emissions, as well as about 30% of a building's energy loss. As such, windows with improved technology for reducing heat loss and solar heat gain can offer significant benefits and cost savings.
Optical filters have also found application in ophthalmic devices to control the light impacting the eye. Opthalmic applications include, for example, prescription and non-prescription glasses, goggles, sunglasses, visors, and safety eyewear.
There are a number of technologies that have been used in optical filters and related devices and applications for dynamically varying the degree of visible light transmittance, including photochromics, electrochromics, liquid crystals, thermochromics, and suspended particle displays.
Electrochromic, liquid crystal, and suspended particle displays or devices may be switched between states of high light transmissibility to one of a lower light transmissibility (or opacity/increased light scattering for some devices) by application of electricity. Such existing power source and wiring may be used in this manner, and may not be inconvenient when a building is designed to accommodate windows or screens comprising such devices, it may necessitate an undesired amount of routing of electrical cables to the device, or cumbersome retrofitting of wiring to accommodate optical filters put in place after a building is constructed. Where the optical filter is used in a wearable device (e.g. opthalmic devices) portability of the power source is an important factor. Thus, devices with a need for high voltage or a bulky power source may not be suitable.
Several concepts for solar-powered windows have been described. For example, U.S. Pat. No. 4,475,031 discloses a sun-sensitive window comprising liquid nematic crystals powered directly by a solar cell. U.S. Pat. No. 5,384,653 discloses an electrochromic window powered by an array of photovoltaic cells deposited along an edge of the window pane. U.S. Pat. No. 5,805,330 discloses an electro-optic window powered solely by photovoltaic cells placed within the window area. U.S. Pat. No. 6,055,089 discloses an electrochromic window powered by photovoltaic cells positioned so that at least part of the incident light on the cells passes through the electrochromic device, providing a form of feedback control. U.S. Pat. No. 6,297,900 discloses a smart window comprising a regenerative photoelectrochromic photovoltaic power source element covering the window area co-extensively with an electrochromic window element.
Some electrochromic devices require continuous power to maintain the dark or faded state, and the power demand may increase with increasing size of the device, particularly windows. For a solar-powered window, a photovoltaic power source with a surface area of sufficient size to meet the device's power requirement may be of an impractical size, and/or prohibitively expensive. If the photovoltaic power source is on a frame or pane of a window or lens, it may interfere with aspects such as window viewability. As photovoltaic power sources are dependent on the available amount of incident light, some lighting conditions may not consistently provide sufficient incident light to generate sufficient power for operation. Finally, even with self-contained photovoltaic power sources, the solutions identified in the past may not provide an adequate means for retrofitting existing buildings with smart window technology.
Therefore there is a need for a solution that overcomes at least one of the deficiencies in the art.